This invention concerns a headlight for vehicles with a bowl shaped reflector having two focal areas and a screen, or shading, shaft arranged between a lens and the reflector, the screen shaft being adjustable to a plurality of rotational positions about an axis of rotation extending horizontally and at a right angle to an optical axis and having a mantle surface with a focal line for each rotational position, which produces a light-dark border of a light figure, or pattern.
Such a headlight for vehicles is disclosed in DE 43 35 286 A1 which has a light system, essentially including an ellipsoidal reflector, a light source disposed at an interior focal area of the reflector, a light collecting lens, and a rotatable stop, or screen, shaft located between the reflector and lens. A gas discharge lamp can serve as a light source. The rotatable screen shaft is coupled to at least one driving mechanism. The axis of rotation of the screen shaft extends horizontally and at a right angle to an optical axis of the light system and is eccentrically aligned to cylindrical mantle-surface portions of the screen shaft. The cylindrical mantle-surface portions of the screen shaft are arranged to be so offset from one another, that the screen shaft has a surrounding step. The driving mechanism makes the screen shaft rotatable to a plurality of positions of rotation. In each position of rotation, the mantle surface forms at its upper portion, a focal line, which creates a light-dark border of a light pattern. Because of the eccentrically disposed axis of rotation, in each position of rotation of the screen shaft, the focal lines extend at a different level of elevation. In this regard, in a plurality of positions of rotation of the screen shaft, an asymmetrical low beam light is emitted. Only in a single position of rotation of the screen shaft is there an optically-effective focal line running in a horizontal plane over its entire length. Thus, only a single symmetrical light bundle is possible. Furthermore, the focal lines, because of the cylindrical mantle surface portions of the screen shaft, cannot assume a desired configuration, as is the case with a stationary screen. It is additionally disadvantageous, that the focal lines, except for a single focal line, when in their active placements relative to a focusing area of the lens, have quite different spacings, due to the eccentric positioning of the axis of rotation relative to the cylindrical mantle surface of the screen shaft. Only a focal line extending through the focusing area of the lens, or near to it, produces a sharp light-dark border, while the other focal lines produce a blurred light-dark border. The unsharpness of the light-dark border grows, the further the focal line is spaced from the focusing area of the lens. For low beams, a fuzzy light-dark border is undesirable, due to glare danger to oncoming traffic.
DE 44 36 684 A1 discloses a headlight for vehicles which, additionally to having a light system with a screen shaft, has a further light system for high beams integrated into the headlight. Since an additional system is necessary for the high beam function, the headlight must be constructed of large size, and a corresponding cost of manufacture is high.
In the case of a headlight disclosed in EP 0 723 108 A1, a first screen plate having two screen edges for producing asymmetric low beams, is pivotal about an axis of rotation; while an additional second stationary screen placed at an appropriate distance from the first screen is required for producing high beam illumination. The first screen plate for low beams extends in its rotational position for long distance illumination, in a horizontal plane. This is disadvantageous, in that only two different low beam bundles are possible and by switching the first screen between the two low beam functions, oncoming traffic is blinded for a short period by the very wide ranging long distance beam.
It is an object of this invention to provide a headlight of the type described in the opening paragraph above in which each focal line of the screen shaft has a desired and exact shape required for a respective light pattern.